A number of alternative approaches have been taken to water distillation that involve a domestic hot water heating tank.
A first approach is to replace the domestic hot water heating tank with a combined hot water and distilled water system. An example of this approach is U.S. Pat. No. 5,304,286 which issued to Palmer in for an invention entitled "Water Supply System" in 1994.
A second approach is to modify an existing water tank by addition of a secondary heating element and a distillation container. An example of this approach is U.S. Pat. No. 4,265,712 which issued to Peter J. McLean in 1981 for an invention entitled "Water Purification System". The McLean patent discloses a water container which is placed on top of a domestic hot water heating tank. The domestic hot water heating tank has been modified to have an additional heating element positioned in a small water chambers. Heated water is provided to the water container from the water chamber within the hot water tank, as required, with flow being controlled by a float valve. Vapour forms in the water container by reason of the high temperature of water within the water container. This vapour rises through a duct and, thereafter, condenses and is discharged into a collection receptacle.
A third approach has been to tap into the hot water tank and use preheated water from the hot water tank in an attempt to make an associated water distiller more efficient. An example of this approach is U.S. Pat. No. 4,549,936 which issued to Erickson in 1985 for an invention entitled "Combination distillation apparatus and hot liquid system". The Erickson patent discloses an evaporation chamber connected to a hot water heater by a first connecting pipe. A second connecting pipe is provided in order that hot water may continuously be cycled from the hot water heater to the evaporation chamber and then back to the hot water heater. A partial vacuum is maintained above the liquid level of the evaporation chamber so that water will boil at a lower temperature. The steam and vapour generated in the evaporation chamber moves upward along a vapour retention pipe that is connected to a condenser.
A fourth approach has been to feed preheated water from a water distillation apparatus into the hot water tank to make the hot water tank more efficient. An example of this is Canadian Patent 1,219,545 issued to Sundquist in 1987 for an invention entitled "Water Heater and Distiller Apparatus". The Sundquist patent discloses a water heater distilling apparatus that receives water directly from the domestic water system of a building and heats it. As the water is heated, steam rises passing through a network of ducting until it condenses into a container. When a demand for heated water arises, water is drawn from the distilling apparatus into a conventional hot water heater. The conventional hot water heater completes the heating of the water for domestic use.
Of the above described approaches, that of Erickson is to be preferred. The approaches of Palmer and McLean are cost prohibitive for they either require a modification of an existing hot water heating tank, or the even more costly replacement of the hot water heating tank with a combination apparatus. The teaching of Sundquist involves placing preheated water into a conventional hot water heating tank. A problem inherent in this approach is that the cycle times of the hot water tank are adversely effected. It is, therefore, preferred to use preheated water from the hot water tank to make the water distiller more efficient.
The Erickson reference also has a number of drawbacks, one of which is its manner of connection to the domestic hot water tank. The manner of connector is complex; requiring a plumber in order to avoid leakage.